Traditional agile spacecraft control architectures use an inertial measurement unit (IMU) on the payload to determine the angular orientation of the payload. Spacecraft also include at least one inertial actuator on the bus for applying torques to the spacecraft to control the sensed orientation of the payload (e.g., to follow a prescribed command). The structural connection between the bus and the payload is typically a hexapod of stiff struts.
To attenuate the transmission of bus vibrations to the payload, these struts are sometimes replaced with passive “isolators,” which provide tuned stiffness and damping to create a mechanical “break.” Because these isolators are located between the inertial actuator and sensor of the attitude control system, the isolators violate co-location protocol and result in an unstable mode. The isolation break frequency must therefore be kept well above the attitude control bandwidth, which minimizes the efficacy of the isolation.
The introduction of an isolated interface also compromises the agility of the spacecraft because high frequency control torques are not passed to the payload. However, agile spacecraft demand control torques whose frequency content not only exceeds the bandwidth of the attitude control system, but also exceeds the break frequencies of the isolation system. This requires active “feedforwards” to high bandwidth torque actuators that are in stiff contact with all parts of the spacecraft.
In some cases, the payload pointing agility required exceeds that of the inertial actuator itself, which is the only source of “inertial torque” available. To meet these demands, the payload should be controlled to move relative to the bus, which results in increased stroke (i.e., displacement) requirements between the payload and the bus.
Accordingly, it is desirable to provide a hybrid actuator for maneuvering a spacecraft payload. In addition, it is desirable to provide a system including a hybrid actuator and an inertial actuator for controlling motion of a spacecraft. Moreover, it is desirable to provide a method for independently controlling a payload and a bus of a spacecraft so that the payload and bus maintain a relative position with respect to one another. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.